Room temperature photoluminescence from Zr-doped sol-gel silica

Intense room-temperature photoluminescence (PL) from the UV to the green region was observed from Zr⁴⁺-doped silica synthesized by a sol-gel process using tetraethoxysilane as the precursor, followed by thermal treatment at 500 °C in air. The wide PL band can be resolved into three components centered at 3.70, 3.25, and 2.65 eV, respectively. The intensity of the 3.25 and 2.65 eV PL bands was greatly enhanced compared with pure sol-gel silica. The 3.70 eV emission was assigned to non-bridging oxygen hole centers, while the 2.65 eV one originated from neutral oxygen vacancies (V_O). The 3.25 eV PL band was most likely associated with E′ centers, as supported by electron spin resonance measurement. It was proposed that the Zr⁴⁺-doping leads to oxygen deficiency in the silica, thus resulting in enhancement of the density of V_O and E′ center defects.